Firstly, this book is much less coherent than "Holy Blood, Holy Grail." (If you did not read that book, do NOT buy this one. HBHG is a wonderful book, pseudo-history at it's best. ML assumes you know the theories laid out in HBHG). The first fourth of the book is just more "proof" of the authors' claims about Jesus. It adds the claim that Timothy was Jesus's twin and that Saint Paul distorted Christianity, but it's not all that interesting.
The second fourth is devoted to vicious (and now dated) attacks against President Ronal Reagan and American fundementalists. The authors, instead of criticising Reagen on his record, choose a barage of name calling.
The second half of the book is a masterpiece. It continues the Holy Blood, Holy Grail story by adding more information. Pierre Plantard figures prominently, and the Priere of Sion is made more "round." If you loved Holy Blood, Holy Grail you will almost love this book. Once you get the first half out of the way it is hard to put down. Though nothing "definitive" is reached, the conspiracy looks even better. When you finish it you wish the book was longer... parting with this book is "such sweet sorrow."
And as always, more cryptic mottos:
Et In Arcadia Ego...
Etats Unis d'Occident 1937-1946